The Mars rover Spirit鈥檚 power levels dropped to an all-time low after a dust storm blanketed its solar panels late last week. NASA is now awaiting a signal from the rover that it survived the ordeal.
Spirit has been silent since Saturday, when a dust storm rendered the atmosphere overhead opaque. Dust deposited on the solar panels cut their capacity from 33 to 27%. And the amount of energy available to the craft dropped to just 89 watt-hours, the lowest level seen since Spirit and its twin, Opportunity, landed on Mars with about 10 times that amount in January 2004.
The storm came little more than a week after similar weather in the far north sent NASA鈥檚 Phoenix lander to an early grave.
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But Spirit may emerge unscathed. 鈥淲e are cautiously optimistic that we can get through this dust storm without a catastrophe,鈥� says rover project scientist Bruce Banerdt of NASA鈥檚 Jet Propulsion Laboratory in Pasadena, California.
That鈥檚 because spring is dawning in the southern hemisphere, where Spirit is located, and the extra sunlight means the rover needs less energy to run its heaters. Had the storm occurred six months ago, during the local winter solstice, the craft would have less chance of survival, says Banerdt.
Maintaining control
On Tuesday, the team commanded Spirit to shut down all unnecessary heaters on the craft and wake up once a day to survey the transparency of the atmosphere.
The hope was to prevent the rover from entering 鈥榣ow-power fault mode鈥�. That would shut down the rover鈥檚 heaters in order to charge its batteries, exposing the craft鈥檚 electronics to extreme cold.
The team will not know for several days whether Spirit received the commands intended to prevent it from entering fault mode. That鈥檚 because to conserve energy, the rover was ordered to wait until Thursday to attempt to contact the Mars Odyssey orbiter, which relays data about the rover鈥檚 health to ground controllers.
Communications blackout
Spirit is parked on the sloping edge of a plateau called Home Plate. The rover鈥檚 solar panels are now tilted by about 22掳 northward, close to the optimal 20掳 needed to maximise sunlight collection during a two-week period from 29 November to 15 December.
At that time, the Sun will lie between Mars and the Earth, preventing communications with the rovers.
The dust storm appears to be clearing, but researchers are not yet sure how much dust will settle onto the rover鈥檚 solar panels, further reducing the available power. The panels could also be cleared by winds, possibly associated with dust devils, as they have been in years past.
Spirit was set to begin moving again after Christmas to its next targets: a hill and small crater some 200 to 300 metres away. But if the new dust on Spirit鈥檚 panels does not clear, the craft may have to remain at its present location for several more weeks or a month, says Banerdt. The added dust could also reduce the number of hours a day the craft could move.
